Fast-access self-repairing tape library using mobile robots

ABSTRACT

In some embodiments, a system includes a plurality of tape reels positioned on a lower surface, a tape drive for reading data from a tape on one of the plurality of tape reels, and at least one mobile robot configured for selectively retrieving at least one of the plurality of tape reels and transporting the at least one retrieved tape reel to the tape drive.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/217,181, filed Aug. 24, 2001, which is herein incorporated byreference.

BACKGROUND

The present invention relates to data storage systems, and moreparticularly, to mobile robots for use in tape libraries.

In magnetic storage systems, data are read from, and written onto, amagnetic recording medium utilizing magnetic transducers. Data arewritten on the magnetic recording medium by moving a magnetic recordingtransducer to a position over the medium where the data are to bestored. The magnetic recording transducer then generates a magneticfield, which encodes the data into the magnetic medium. Data are readfrom the medium by similarly positioning the magnetic read transducerand then sensing the magnetic field of the magnetic medium. Read andwrite operations may be independently synchronized with the movement ofthe medium to ensure that the data can be read from, and written to, thedesired location on the medium.

In a tape drive system, magnetic tape is moved over the surface of thetape head at high speed. Usually the tape head is designed to minimizethe spacing between the head and the tape. The spacing between themagnetic head and the magnetic tape is crucial so that the recordinggaps of the transducers, which are the source of the magnetic recordingflux, are in near contact with the tape to effect writing sharptransitions. Also when the read element is in near contact with thetape, effective coupling of the magnetic field from the tape to the readelement is possible.

In the near future, with the adoption of improved media, the cost ofstoring information (on a per byte basis) on tape is expected to declineby a factor of five or more with respect to magnetic disk. Also,short-term and long-term reliability will continue to favor tape-basedstorage. Furthermore, as more mass storage is allocated to cloudnetworks, most storage will be in large libraries, rather than onindividual drives, which is a consideration favoring tape-based storage.One disadvantage of tape-based storage with respect to disk-basedstorage is the relatively poor access time associated with tape-basedstorage, with the time required to bring the tape to the tape drive andthen spool the tape to the file location typically averaging about 40seconds. If the access time could be reduced, tape-based storage wouldbe better positioned versus disk-based storage for storing files around10 MB and greater, such as photographs, videos, collections, etc., whichare accessed only rarely, but which users want to be able to retrievealmost immediately, e.g., within about a second.

BRIEF SUMMARY

In one embodiment, a system includes a plurality of tape reels, a tapedrive configured for reading data from tape stored on at least one ofthe plurality of tape reels, a mobile robot having a volume of less thanabout 1000 cubic inches, the robot configured for selectively retrievingone or more of the plurality of tape reels and transporting the one ormore retrieved tape reels to the tape drive, wherein the robot movesunconstrained along a first surface, and a controller for directingmovement of the robot.

Such embodiment may be implemented in a magnetic data storage systemsuch as a tape drive system, which may include a magnetic head, a drivemechanism for passing a magnetic medium (e.g., recording tape) over themagnetic head, and a controller electrically coupled to the magnetichead.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic diagram of a simplified tape drive systemaccording to one embodiment.

FIG. 2 illustrates a system using mobile robots for faster access totape, according to one embodiment.

FIG. 3 shows a more detailed view of a mobile robot, according to oneembodiment.

FIG. 4A illustrates an optical pattern on a surface, according to oneembodiment.

FIG. 4B illustrates a surface design, according to one embodiment.

FIG. 4C illustrates a surface design, according to one embodiment.

FIG. 4D illustrates a surface design, according to one embodiment.

FIGS. 5A-5B show detailed views of a mobile robot, according to oneembodiment.

FIGS. 6A-6B show detailed views of a tape library using mobile robots,according to one embodiment.

FIGS. 7A-7D illustrate tape threading using a mobile robot, according toone embodiment.

FIGS. 8A-8D show steps of self tape threading using a tape drive,according to one embodiment.

FIGS. 9A-9C show steps of using flange extenders, according to oneembodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof.

In one general embodiment, a system includes a plurality of tape reels,a tape drive configured for reading data from tape stored on at leastone of the plurality of tape reels, a mobile robot having a volume ofless than about 1000 cubic inches, the robot configured for selectivelyretrieving one or more of the plurality of tape reels and transportingthe one or more retrieved tape reels to the tape drive, wherein therobot moves unconstrained along a first surface, and a controller fordirecting movement of the robot.

In another general embodiment, a system includes a plurality of tapereels positioned on a lower surface, a tape drive for reading data froma tape on one of the plurality of tape reels, at least one mobile robotconfigured for selectively retrieving at least one of the plurality oftape reels and transporting the at least one retrieved tape reel to thetape drive, wherein the at least one mobile robot moves unconstrainedalong an upper surface that overlies the plurality of tape reels, and acontroller for directing movement of the at least one mobile robot.

FIG. 1 illustrates a simplified tape drive 100 of a tape-based datastorage system, which may be employed in the context of the presentinvention. While one specific implementation of a tape drive is shown inFIG. 1, it should be noted that the embodiments described herein may beimplemented in the context of a variety of tape drive systems.

As shown, a tape supply cartridge 120 and a take-up reel 121 areprovided to support a tape 122. One or more of the reels may form partof a removable cartridge and are not necessarily part of the system 100.The tape drive, such as that illustrated in FIG. 1, may further includedrive motor(s) to drive the tape supply cartridge 120 and the take-upreel 121 to move the tape 122 over a tape head 126 of any type. Suchhead may include an array of readers, writers, or both.

Guides 125 guide the tape 122 across the tape head 126. Such tape head126 is in turn coupled to a controller assembly 128 via a cable 130. Thecontroller 128 typically controls head functions such as servofollowing, writing, reading, etc. The controller may operate under logicknown in the art, as well as any logic disclosed herein. The cable 130may include read/write circuits to transmit data to the head 126 to berecorded on the tape 122 and to receive data read by the head 126 fromthe tape 122. An actuator 132 controls the position of the head 126relative to the tape 122.

An interface 134 may also be provided for communication between the tapedrive and a host (integral or external) to send and receive the data andfor controlling the operation of the tape drive and communicating thestatus of the tape drive to the host, all as will be understood by thoseof skill in the art.

As shown by the partial top down view of FIG. 2 and the cross-sectionalview of FIG. 3, a system 200, such as a tape library, may include one ormore mobile robots 210 for transporting at least one tape reel 202,which may or may not be part of a tape cartridge, to and from tapedrives 204 for reading data from the tape. The tape on the selected tapereel or pair of tape reels may be accessed by the mobile robots 210,which may be miniature remote-controlled vehicles that move on a surface(such as an upper surface 302, used interchangeably with the term“ceiling,” as shown in FIG. 3). Thus, the tape reels may lie on a lowersurface, such as a “floor,” while a mobile robot maneuvers on the uppersurface unconstrained, e.g., without the use of rails, tracks, pathways,etc., such as through magnetic attraction between the robot and theupper surface or portions of the upper surface (see FIG. 3). In oneapproach, the tape library may comprise more than one level. On eachlevel, tape reels may be arranged on a lower surface (usedinterchangeably with the term “floor”) in a dense pattern. Thisarrangement is shown in partial top down view of FIG. 2, according toone embodiment.

A contiguous tape may be stored on a single reel, and may include a pinor other end piece that enables threading of the tape in the tape drive.In other approaches, the tape may be coupled to a pair of reels, e.g.,in a tape cartridge.

According to one embodiment, magnetic tape may be included in miniaturetape reels 202 which have only a fraction of the tape length of astandard tape cartridge, thereby decreasing seek time. Such shorterlength may be, e.g., less than about ⅕th the tape length of a standardLinear Tape Open (LTO) tape cartridge, less than about 1/25^(th) thetape length of a standard tape cartridge, less than about 1/50th thetape length of a standard tape cartridge, etc. In some approaches, alength of tape on the plurality of tape reels 202 may be less than about50 meters for each tape reel 202, and may be preferably less than about25 meters, more preferably 20 meters or less, etc.

The seek time of tape-based systems using such tape reels may also oralternatively be decreased by increasing the locate speed, e.g., toabout 20 meters per second (m/s) or faster. “Locate time” refers to thetime required for the tape to wind to the beginning of a data set (orfile) after the tape is loaded in the tape drive. If the tape length isreduced to about 20 m or less and the locate speed is about 20 m/s, theaverage locate time is (20 m/20 m/s)/2=0.5 s. In addition to decreasingthe seek time in the drive, the system seek time may be reduced bystructuring the tape library to achieve a mean load time of about 0.5 s.“Load time” refers to the time between the first time when a requestreaches the tape library and a second time when the relevant tapereel(s) are loaded in the tape drive.

According to one embodiment, the tape system is configured such that theaverage seek time is less than about 2 seconds, preferably about 1second or less. The seek time is the delay between a first time when arequest to access data is received by the tape library, and a secondtime when the tape library begins to provide the data to the requester.

With continued reference to FIG. 2, the tape reels 202 may be closelypacked, for example in a hexagonal array, ordered array, circulararrangement, etc., to maximize the number of tape reels that may bestored in a limited amount of space.

According to one embodiment, a diameter of each of the plurality of tapereels 202 may be less than about 100 mm, such as less than about 50 mm,less than about 40 mm, less than about 30 mm.

In some approaches, a single tape drive 204 is available for readingand/or writing tape on the tape reels 202. Depending on the frequencywith which files are read, a plurality of tape drives 204 may beavailable for reading and/or writing tape on the tape reels 202, asshown in FIG. 2 by the leftmost tape drive 204 reading a tape. The tapedrives 204 may be located about the surface in any arrangement as wouldbe known to one of skill in the art, preferably such that quick accessto the tape drives 204 is possible to reduce loading and data accesstimes.

In one approach, the system 200 may be configured to permit the mobilerobot 210 to locate, retrieve, and transport any one selected tape reel202 to the tape drive 204, and to initialize reading of the tape by thetape drive 204 within about five seconds of receiving a request to readdata from the tape of the selected tape reel 202, more preferably withinabout 2 seconds, and ideally less than about 1 second.

In several embodiments, several mobile robots 210 move unconstrainedalong the surface, e.g., two, five, or more. In other embodiments, onlya single robot may be present on a given level. It may be advantageousfor the robots 210 to be unconnected by cables to any other part of thesystem 200. This design favors fast robot motion, and facilitates therobots 210 being capable of moving between levels, rooms, enclosures,etc.

Also, when multiple robots 210 are used, any problem with cables gettingtangled together from different robots 210 is eliminated when the robots210 are controlled wirelessly.

The mobile robots 210 may have predetermined “resting” locations, asshown by mobile robots 210, according to one embodiment. As shown inFIG. 2, mobile robot 211 has moved from a resting location, acquiredtape reels, and is moving toward a tape drive to load the tape reels inthe tape drive for reading tape therefrom. Also, mobile robot 208 hasretrieved tape reels from a tape drive which has completed a readingoperation, and is returning the tape reels to their storage location. Ofcourse, this movement is exemplary only, and not meant to be limiting onthe invention in any way.

The mobile robots 210 may move in straight line increments, or may movemore naturally in arcing patterns between positions on the surface,according to various embodiments. Also, the mobile robots 210 may avoidobjects in their path according to any method as would be understood byone of skill in the art upon reading the present descriptions.

In some previous tape library geometries, a library gripper accesses anarray of tape reels and/or tape cartridges, through motion of a firstcarriage along a rail or pair of rails. The first carriage in turn holdsanother set of rails or guides which enables motion of a second carriageholding the gripper. The scheme enables the gripper to access anywherein two dimensions, where the tape reels or tape cartridges are located.Alternately, in some previous designs, the second carriage has beenreplaced by a rotary motion which operates about the axes of the firstcarriage. This scheme limits the flexibility of the library, becausegrippers (or robots) may interfere with one another. For example, if thegrippers use the same set of rails, then they cannot move past eachother. Also, there is generally no available space in tape libraries forthe installation of an additional set of rails, so this scheme isseverely limited in its functionality. In addition, these previousdesigns do not facilitate easy recovery of access to the tape reelsand/or tape cartridges when a gripper fails.

On the other hand, the systems herein use “unconstrained” robots, whichfacilitate access to the tape reels and/or tape cartridges. Here, theterm “unconstrained” indicates that movement is not constrained torails, tracks, guideways, pathways, etc., but instead movement is freein at least two dimensions, e.g., along a surface. Thus, unconstrainedmobile robots are easily added or removed from the surface, and they caneasily maneuver around each other along the surface, since they are notfixed to a rail or track.

As shown in FIG. 3, according to one embodiment, the surface acrosswhich the mobile robots 210 travel unconstrained may be an upper surface302 (such as a ceiling in one approach) and may be unpatterned so thatthe mobile robots 210 are unconstrained, e.g., not limited to motion onparticular tracks, paths, rails, etc. Thus each mobile robot 210 iscapable of movement independent of movement of any other mobile robot210, e.g., each mobile robot 210 may cross the path that any othermobile robot 210 has taken or will take. Similarly, by attaching themobile robot 210 to a surface 302 separate from a surface 304 supportingthe tape reels 202, the mobile robots 210 are not constrained to followaisles, paths, corridors, etc., between groups, columns, rows, etc., oftape reels 202. In one example, this movement may be analogous to themovement of a shopping cart through a supermarket. However, instead ofbeing constrained to moving between the shelves of the supermarket, themobile robots 210 are capable of moving unconstrained along the ceilingof the supermarket, capable of selecting any desired item from below inthe shelves, as an example. The ability to use multiple mobile robots210 to access a group of tape reels 202 provides faster access of short,popular files. This geometry is much more flexible than previousconfigurations, in which the tape cartridge grippers were supported on xand y positioners which could not cross paths. The mobile robots 210 maybe coupled to the upper surface 302 using magnets 310 or some othercoupling or attraction device that biases the mobile robots 210 towardsthe upper surface 302. By allowing the mobile robots 210 to maneuver onthe upper surface 302, the tape reels 202 may simply rest on a lowersurface 304, such as a floor. The magnets 310 may bias the mobile robot210 toward the upper surface 302 with much more force than gravitybiases the mobile robot 210 toward the lower surface 304, allowing amuch higher frictional force of the mobile robot wheels 306, 308,thereby enabling faster robot acceleration and thus faster seek times.

In one approach, the mobile robot 210 may have three wheels 306, 308:two rear wheels 308 and one front (maneuvering) wheel or ball 306. Inanother three-wheel configuration, the mobile robot 210 may have twofront wheels 308, and a rear (maneuvering) wheel or ball 306. For sakeof clarity, a maneuvering wheel in this discussion indicates a wheelwhose direction of positioning or rotation with respect to the robotbody is not fixed. Of course, the mobile robot 210 may have any numberof wheels 306, 308 or other apparatus for causing movement of the mobilerobot 210 as would be known to one of skill in the art. Steering of therobot may be accomplished in any known manner, such as by independentlydriving two of the wheels with a caster maneuvering wheel, steeringusing the maneuvering wheel, and driving and steering with themaneuvering wheel, etc.

The mobile robot 210 may have a reel gripper 312, which when the mobilerobot 210 is positioned above a desired tape reel 202 or set of tapereels 202, may grab, attract (for example, magnetically), secure, orotherwise take hold of the tape reel 202 such that it may be loaded intothe mobile robot 210 and transported to a tape drive or back from a tapedrive to the tape reel's storage location.

With continued reference to FIG. 3, in some embodiments, the mobilerobot 210 may have a height such that it may be able to maneuver abovethe tape reels 202 in a space H of about 1.75″, which measures about 1Uin a standard rack configuration. The smallest units used forrack-mounted computer components are “1U” units, which are 1.75″ high.Since a reel for standard 0.5″ wide magnetic tape may be as thin as0.58″, this 1U unit may be thick enough to hold a single layer ofstorage having a layer of tape reels 202 plus mobile robots 210. Thus asingle layer design having mobile robots 210, tapes 202, and drives maybe used for various tape library configurations, ranging from a singlelayer to multiple stacked layers, which may fill an entire storage room,or any size desired.

In one approach, the plurality of tape reels 202 may be spaced from andlocated within a distance of about 15 cm from the upper surface, e.g.,15±1.5 cm, less than about 20 cm, less than about 10 cm, less than about5 cm, or any value in the foregoing ranges.

The system 200 may also comprise a controller 212 for directing movementof the robot 210. The controller 212 may be on board the robot 210, oraway from the robot 210 (as shown in FIG. 2) and in communicationtherewith via any type of communication channel (such as wireless,wired, infrared, etc.).

According to one illustrative embodiment, a system 200 comprises atleast one tape drive 204 configured for reading data from tape stored onone of a plurality of tape reels 202, at least one mobile robot 210having a volume of less than about 1000 cubic inches (and in someapproaches less than about 900 in³, less than about 750 in³, less thanabout 500 in³, less than about 250 in³, less than about 100 in³, lessthan about 50 in³) configured for selectively retrieving one or more ofthe plurality of tape reels 202 and transporting the one or moreretrieved tape reels 202 to the tape drive 204. The mobile robot 210moves along a surface, and is preferably not mechanically constrained tomove along a pre-determined trackway or path (i.e., it isunconstrained). In some approaches, the robot 210 may be mechanicallyunconstrained and may be able to move autonomously across the surfacevia any desired path.

To assist in navigation of the mobile robot 210, at least one of thelower and upper surfaces may include an optical pattern usable fornavigation of the mobile robot 210, and the mobile robot 210 may beconfigured for recognizing the optical pattern.

As shown in FIG. 4A, the lower surface or floor 304, for example, mayinclude an optical pattern 402 designed for the mobile robot to locateits position. This optical pattern 402 may be a rectangular gridextending over the entire floor 304, with each grid square 404 labeledwith readable code identifying the row and column of the particular gridsquare 404. This readable code may take any form as would be understoodby one of skill in the art.

The floor 304 may be planar, as shown in FIG. 4B, covered with smallindentations as shown in FIG. 4C, or have a lattice defining receptacleareas in which the tape reels 202 are positioned as shown in FIG. 4D,according to various embodiments. By extending the lattice up past thetape reels 202, it may form a surface on which the mobile robot 210 maybe supported, and the mobile robots 210 would not maneuver along theupper surface but instead would maneuver on the lower surface formed bythe top surface of the lattice, according to one embodiment.

The design of the mobile robot 210 may include additional features,abilities, etc., as would be understood by one of skill in the art uponreading the present descriptions. In one embodiment, a mobile robot 210is shown in FIGS. 5A-5B, according to one approach. In this example, oneor more motors 508 power symmetric drives wheels 308 that allow forwardand backward motion, and in a further approach, the drive wheels 308 mayprovide steering if the drive wheels 308 are operated independentlyusing two symmetric drive motors 508. These motors 508 may be attachedto each wheel 308 by a single step-down gear. The mobile robot 210 mayadditionally be supported by one or more other omni-directional passivewheels 306, which may move in any direction, and may be maneuverable(e.g., steerable, positionable, etc.), in some approaches. Theomni-directional wheel(s) 306 may be caster wheels, and more preferablymay be spherical balls which are also referred to as ball transfers.

To pick up the tape reel(s) 202, a simple platform 312 may be loweredand raised by a solenoid or motor (not shown). If the tape reels 202 aretopped by a magnetic plate, the tape reels 202 may be gripped to theplatform 312 by energizing electromagnets 502. One or more cameras 504may allow for navigation of the mobile robot 210. A camera 504 may beplaced above each reel holding position 506, enabling the mobile robot210 to determine its position and to deliver a tape reel 202 directlyinto a tape drive. The mobile robot 210 need not be made precisely,because the cameras 504 may simultaneously image the tape reels 202 andlocation grid (or the tape reel chucks on the drive) to preciselyposition the tape reels 202, in some approaches.

To enable multiple mobile robots 210 to work in the same work space,such as the same floor, there are preferably no cables attached to themobile robots 210. The mobile robot 210 uses little power, and a peakspeed of about 2 m/s in some embodiments is sufficient to pick up thetape reel 202 and bring it to the drive within a half second. For a 150gram mobile robot 210, the corresponding kinetic energy would be about0.3 Joule. This amount of energy may be supplied by a rechargeablebattery, through inductive coupling, etc., but a capacitor, with itsextremely long lifetime, may be preferable. In one embodiment, an 80volt, 1000 μF electrolytic capacitor which includes 3.2 Joules, yet isonly 16 mm diameter by 40 mm long may be used. The mobile robot 210 maybe recharged at its parking position, or at the tape drive when it loadsthe tape reel 202.

As shown in FIG. 5B, according to a preferred embodiment, the tape reels202 are positioned on a floor 304, the surface 302 is opposite the floor304, and the mobile robot 210 is biased toward the surface 302, such asthrough magnetic biasing (by using magnets 310), thereby suspending therobot 210 above the tape reels 202. For example, the mobile robot 210may be magnetically biased toward the upper surface 302.

As shown in FIGS. 6A-6B, a library controller may communicate with themobile robots 210 by light, such as infrared (IR); radio frequency (RF);etc., and may be differentiated on each level of the library 200 toavoid cross-talk. The library controller computes a path the mobilerobot 210 is to take to pick up and drop off the tape reels and load thetape reels in the tape drives 204. The mobile robot 210 may servo alongthe path by using its cameras, in one approach, or it may use encoderson its motors or wheels to servo, using the cameras only for fineadjustments, in another embodiment.

In one embodiment, the tape library 200 may comprise a plurality of tapedrives 204, where each tape drive 204 is positioned on the floorsupporting the tape reels, the floor being below the surface on whichthe mobile robots 210 maneuver by a distance sufficient to allowmovement of the mobile robots 210 therebetween (between the tape reelsand the surface).

In large multilayer libraries 200, mobile robots 210 may move betweenfloors using ramps 604. This enables the mobile robots 210 themselves toload different floors with tape reels, and to rebalance the work load byoptimally locating the mobile robots 210 and organizing the tape reels.The relative number of mobile robots 210, tape reels, and tape drives204 may be determined by the access frequency of the files, data, etc.

According to one approach, multiple surfaces having a spaced and stackedconfiguration may be used, and the mobile robot 210 is configured totravel between the multiple surfaces. In this approach, at least oneramp 604 may be provided, connecting at least two of the multiplesurfaces, thereby permitting the mobile robot 210 to travel between themultiple surfaces. In these or any other approaches, there may be nocable coupled between the mobile robot 210 and any other component ofthe system.

As illustrated in FIG. 6B, according to one embodiment, one or more tapedrives 204 may be secured directly to the floors 606 of a tape library200 having one or more levels. In addition, the mobile robots 210 may beattracted to the ceilings 602. In this design, the drive(s) 204 may beeasily positioned at any location in the tape library 200 by simplyleaving space in the array of reels (not shown). This arrangementfacilitates reconfiguration of the tape library 200 after it has beenmanufactured, along with replacement of failed tape drives should theyoccur. For example, the mobile robots 210 may be adapted for movingand/or relocating a tape drive 204. At least one tape drive 204 may bepositioned on each level of the tape library 200, according to oneembodiment.

The library can be configured to have “spare” tape drives 204 and mobilerobots 210 ready to be put into use upon failure of other tape drivesand mobile robots, according to one embodiment. In another embodiment,when extra tape drives 204 or mobile robots 210 are to be used, due tosome factor, such as an increased work load, failed mobile robots and/ortape drives, etc., the tape library 200 may allow adding or removingtape drives, tape reels, and/or mobile robots by the user aftermanufacture of the tape library 200.

Any type of tape threading system known in the art may be adapted foruse with the systems described herein, according to various embodiments.For example, if tape reels are used individually (not as pairs), astandard threader mechanism may be used to thread the tape reel onto thetape drive, according to one embodiment. Storing the tape on pairs ofreels has an advantage in that after loading, the tape is ready to beused and does not need to be wound onto another inboard reel. Also, whenthe tape is finished being used, both reels may be removed with thetape, and the tape does not need to be unwound from the inboard reel inorder to be removed.

In another embodiment, as shown in FIG. 7A, the tape drive 204 itselfmay have no threader. Rather, the mobile robot 210 may be configured tothread tape 706 of the retrieved tape reel 702 onto the tape drive 204.In one approach, a mobile robot 210 loads the tape 706 provided on apair of tape reels 704, 704, by first dropping off one reel 702 on thedrive 204, and then the other reel 704 on a reel chuck 708, for which areel motor may wind the tape 706. Alternately, if the tape 706 is storedon one reel only (such as reel 702), the mobile robot 210 may move anend of the tape not on the reel 702 to secure it to the inboard drivewheel, as described in relation to FIGS. 7B-7D. The precision of themobile robot 210 motion may be much greater than that of a leader pinloader mechanism currently used in tape drives, in some approaches.

In another embodiment, as shown in FIGS. 7B-7D, a single reel 702 oftape 706 may be loaded onto a reel chuck and motor 714 which are fixedto a carriage 716 that is adapted to follow a guide 718 that allows formotion of the chuck 714 around the tape drive 204 to facilitatethreading of the tape 706. Before loading the reel 702 on the chuck 714,the chuck 714 is brought into proximity of the inboard (take-up) reel710, as shown in FIG. 7B. After the mobile robot (not shown for clarity)places the reel 702 on the chuck 714, a mechanism 712 attaches the endof the tape 706 to the take-up reel 710. See FIG. 7C. At this point, thetape 706 may be transferred between reels 702 and 710 as part of apreliminary locate operation, before the tape 706 contacts the recordinghead 720 or any guide surfaces, such as rollers, thus enabling fastertape locate with reduced tape damage and drive wear. Then, the chuck andreel motor 714 and tape reel 702 are moved along the guide 718 to afinal position, as shown in FIG. 7D, where the tape 706 may be read fromor written to.

In another embodiment, rather than moving the library reel 702 andcarriage 716, the take-up reel 710 and its motor may be moved to threadthe drive 204. In yet another embodiment, if the tape 706 is stored on apair of reels, the mobile robot may position the two reels directly onthe tape drive 204, where the tape 706 may be located before threading.

Alternatively, as shown in FIGS. 8A-8D, the tape 706 may be held on twotape reels 202, and a method may be used which avoids the unreliabilityof a leader pin. In this approach, the reel drive chucks 802 may bespaced with the same close spacing of the tape reels 202 in theirstorage position. The mobile robot places the tape reels 202 on thechucks 802, as shown in FIG. 8B, and two moveable rollers 804, 806sequentially thread the tape 706 in position. First, roller 804 threadsthe tape 706, as shown in FIG. 8C, and then roller 806 threads the tape706, as shown in FIG. 8D. The tape 706 may locate before the rollers804, 806 move into their final position, thus avoiding the extra wearand control difficulties associated with contact of the tape 706 withthe roller 806 or other guide surfaces and the head. Alternately, twosmooth cylinders which form air bearings may be used to thread the tapedrive, in another embodiment.

In one embodiment, each reel may be large enough (e.g., the flanges arebig enough) to hold the entire length of tape, if all the tape is to beaccessed. If the tape is stored in pairs of these large reels, thecapacity of the library may be reduced by a factor of two from what itmay be by using single reels.

In another approach, the tape may be stored on a pair of reels, where atleast one reel is not large enough to accept the entire length of tape.As shown in FIGS. 9A-9C, a reel-size reduction may be effected byincorporating temporary flange extenders 902, 904 in the tape drive. Inthe tape drive, a temporary flange extender 902 is fixed to themotor/reel chuck 908 so that the reel flange 906 is extended when it ison the drive. Once the reels 202 are in the drive, another flangeextender 904 is placed on the top of each of the reels 202, so that tapecan be spooled onto one of the reels. Before the tape reels 202 areunloaded from the tape drive, the tape is spooled back evenly betweenthe tape reels 202, so that it lies only between the permanent flanges906 on the tape reels 202.

In another approach, a packing roller may be used to keep the tape onthe reel after its diameter becomes bigger than the flange.

In some approaches, the tape library may be fault tolerant and/or selfrepairing. For example, each tape cartridge may be read by a number ofdifferent drives, if a robot fails then other robots may maneuver aroundthe failed robot, a failed robot may be towed away by another robot andreplaced, and/or a failed tape drive may be towed away and replaced.

According to one embodiment, if a mobile robot fails, it may be towedaway and replaced by another mobile robot. The tape drives may beconfigured so that a mobile robot may easily tow away and replace a tapedrive, after temporarily clearing away the tape reels that may be in thepath taken to remove the tape drive. The power and data connections maybe made to use very little force, for example, using simple slidingspring contacts for the power and optical link for the tape drive datatransfer.

According to one embodiment, the system may be configured to allowremoval of a failed mobile robot using another mobile robot, in whichcase the failed mobile robot may then be replaced with the mobile robotperforming the removing or another mobile robot, in some approaches.

In another embodiment, the mobile robot may be configured to remove thetape drive, e.g., if the tape drive is broken. Likewise, the robot mayinstall a replacement or repaired tape drive.

It will be clear that the various features of the methodologies andembodiments described herein may be combined in any way, creating aplurality of combinations from the descriptions presented herein.

Communications components such as input/output or I/O devices (includingbut not limited to keyboards, displays, pointing devices, etc.) may becoupled to the system either directly or through intervening I/Ocontrollers.

Communications components such as buses, interfaces, network adapters,etc., may also be coupled to the system to enable the data processingsystem, e.g., host, to become coupled to other data processing systems,remote printers, storage devices, etc., through intervening private orpublic networks. Modems, cable modems, and Ethernet cards are just a fewof the currently available types of network adapters that maybe used, insome approaches.

It will be further appreciated that embodiments described herein may beprovided in the form of a service deployed on behalf of a customer tooffer service on demand.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A system, comprising: a plurality of tape reels;a tape drive configured for reading data from tape stored on at leastone of the plurality of tape reels; a mobile robot having a volume ofless than about 1000 cubic inches, the robot configured for: selectivelyretrieving one or more of the plurality of tape reels; and transportingthe one or more retrieved tape reels to the tape drive, wherein therobot moves unconstrained along a first surface; and a controller fordirecting movement of the robot.
 2. A system as recited in claim 1,wherein the plurality of tape reels are supported by a second surfacelocated within about 15 cm of the first surface, and wherein the firstsurface is different than the second surface.
 3. A system as recited inclaim 1, wherein the system is configured to permit the mobile robot tolocate, retrieve, and transport any one selected tape reel to the tapedrive, and to initialize reading of the tape by the tape drive withinabout five seconds of receiving a request to read data from the tape ofthe selected tape reel.
 4. A system as recited in claim 1, wherein atleast two mobile robots move along the first surface.
 5. A system asrecited in claim 1, where the tape is stored on a pair of tape reels. 6.A system as recited in claim 1, wherein at least five mobile robots movealong the first surface.
 7. A system as recited in claim 1, wherein thesystem is configured to allow removal of a failed mobile robot usinganother mobile robot.
 8. A system as recited in claim 1, wherein themobile robot is adapted for moving and/or relocating a tape drive.
 9. Asystem as recited in claim 1, wherein the tape reels are positioned on afloor, wherein the first surface is opposite the floor, the mobile robotbeing biased toward the first surface.
 10. A system as recited in claim9, wherein the mobile robot is magnetically biased toward the firstsurface.
 11. A system as recited in claim 9, wherein at least one of thefloor and the first surface includes an optical pattern usable fornavigation of the mobile robot, and wherein the mobile robot isconfigured for recognizing the optical pattern.
 12. A system as recitedin claim 9, wherein the floor has at least one of: i) a planar surfaceupon which some of the plurality of tape reels are positioned, ii) anindented surface in which some of the plurality of tape reels arepositioned in the indentations, and iii) a lattice defining receptacleareas in which some of the tape reels are positioned in the receptacleareas.
 13. A system as recited in claim 12, further comprising aplurality of tape drives, wherein each tape drive is positioned on thefloor supporting the tape reels, the floor being below the first surfaceby a distance sufficient to allow movement of the mobile robotstherebetween.
 14. A system as recited in claim 1, further comprisingmultiple surfaces having a spaced and stacked configuration, wherein themobile robot is configured to travel between the multiple surfaces. 15.A system as recited in claim 14, further comprising at least one rampconnecting at least two of the multiple surfaces for allowing the mobilerobot to travel between the multiple surfaces.
 16. A system as recitedin claim 1, with a proviso that no cable is coupled between the mobilerobot and any other component of the system.
 17. A system as recited inclaim 1, wherein the mobile robot is configured to thread tape of theretrieved tape reel onto the tape drive.
 18. A system as recited inclaim 1, wherein each tape reel has a length of tape thereon of lessthan about 50 meters.
 19. A system as recited in claim 1, wherein eachtape reel has a diameter of less than about 50 mm.